Polarization of Luminescence in the Nanostructure Si/CaF<Subscript>2</Subscript> Upon Polarization of the Nuclear Spins of Fluorine

The laws governing polarization of luminescence in the nanostructure Si/CaF₂ upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically. The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅10⁷ to 3⋅ 10⁸ sec⁻¹ with the CaF₂ layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 524–529, July–August, 2005.     

Recombination processes in europium-doped cadmium iodide crystals

Results of comprehensive research into optical and luminescent-kinetic characteristics of europium-doped cadmium iodide crystals excited by nitrogen laser radiation, α-particles, and x-rays are presented. Crystals under study have been grown by the Bridgman–Stockbarger method. The doping EuCl₃ admixture was introduced into the charge in quantities of about 0.05 and 1.0 mol%. Impurity absorption detected in the near-edge region of the crystals is interpreted as part of the Eu²⁺ ion long-wavelength band associated with f–d-transitions. The cation impurity and matrix defects in CdI₂:Eu²⁺ crystals create complex centers responsible for emission with a maximum in the 580–600-nm region. The short component in the luminescence decay kinetics of weakly-doped crystal excited by α-particles and x-ray photons is due to the exciton emission characteristic of CdI₂. The slow component in the scintillation pulse results from recombination of charge carriers followed by creation of exciton-like states on the defect-impurity centers. Laser or x-ray excitation induces light-sum accumulation on the trapping levels at a depth of 0.2–0.6 eV that is mainly related to matrix microdefects. Trapping centers associated with the chlorine impurity are observed in the heavily-doped crystal. Photostimulated luminescence at 85 K arising at the electron stage of the recombination process is caused by recombination of electrons released from F-type centers with holes localized near the activator. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 358–364, May–June, 2009.     

Doppler spectroscopy of a beam in the channel of a H− ion source

It is shown that high-accuracy contact-free measurements of the divergence and emittance of an accelerated H⁻ ion beam at the exit from the source can in principle be performed by passive Doppler spectroscopy of a beam of excited hydrogen atoms produced by neutralization of the ions with excitation on the residual gas in the source channel. The intensity of the H_α-line radiation detected by the Doppler system is calculated, taking into account the principal processes leading to the excitation and deexcitation of the 3s, 3p, and 3d levels of the hydrogen atoms in the beam, for residual gas densities of the order of 10⁻⁴–10⁻⁵ Torr in the source channel. The computed H_α-line intensity was confirmed experimentally, making it possible to perform photoelectronic detection of the spectral contour of the line in the current mode rather than the photon-counting mode. Zh. Tekh. Fiz. 68, 15–18 (June 1998)     

Slow components of the emission decay in fluoride crystals doped with Ce3+

Spatially separated defects created by photons with energies 6–8 eV in alkali-earth fluoride crystals doped with cerium are investigated with the help of thermoluminescence. Measuring the spectra of creation of V_k and H peaks of thermostimulated luminescence inBaF ₂:Ce³⁺. we demonstrate that photons with energies higher than 6eV induce H centers (self-trapped holes captured by interstitialF ions), whereas the formation of self-trapped holes begins on exposure to photons with energies greater than 7 eV. The influence of photoionization on theCe ³⁺ luminescence inBaF ₂, SrF₂, CaF₂, andCeF ₃ crystals is investigated in the range of photon energies 4–8 eV. An exponentialCe ³⁺-emisson decay was observed for excitation energy lying in the range 4–6 eV. Slow and fast decay components were observed under excitation by photons with energies higher than 6 eV. We believe that the slow and fast components are due to the tunnel recombination of trapped electrons with hole centers. A. P. Vinogradov Institute of Geochemistry of the Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 43–49, March, 2000.     

Luminescence and lasing properties of neodymium- and uranium-activated inorganic laser liquids

An attempt was made to describe and show the possibilities of new inorganic neodynium- and uranium-activated laser liquids: SO₂-GaCl₃-NdCl₄; SO₂Cl₂-GaCl₃-NdCl₃-UO₂Cl₂; POCl₂-MCl_n-NdCl₃-UO₂Cl₂ for development and synthesis of direct nuclear reaction-excited lasers. Luminescence data presented in the work were used to calculate the luminescence parameters of the laser liquids such as oscillator strengths f, probability of spontaneous radiation A, intermultiplet luminescence branching coefficient β, cross-section for induced radiation σ, luminescence decay time τ, quantum yield η, and others. It is shown that the oscillator strengths of the normal absorption bands of Na³⁺, which play the main part in the pumping processes, exceed the oscillator strengths of Na³⁺ for aqueous and many other nonaqueous systems. In the luminescence excitation spectra of the Na³⁺ ion, bands are isolated in the range 400–1000 nm atλ _rec =1.06 μm. With excitation, luminescence occurs through the⁴F_3/2→⁴I_{9/2,11/2.13/2} channels. Luminescence spectral data are related to the lasing parameters. The threshold lasing energy is∼18 J/cm³. For a resonator with mirros h₁=100% and h₂=20, 40, 56, and 80%, the lasing energy is∼20–120 MJ/cm³ in the pumping energy range 18–180 J/cm³. The differential efficiency is ∼0.2% The substantial angular radiation divergence (θ∼4·10⁻² rad) and strong thermostatic distortions that occur in the active element (dn/dT≈−1.9·10⁻⁴K⁻¹) are a disadvantage of laser liquids. It is shown that operation of neodymium- and uranium-activated inorganic liquid lasers is stable under the present conditions. A. I. Gertsen Russian State Pedagogical University, Moika Embankment, 48, St. Petersburg, 191186, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 607–619, September–October, 1997.     

Use of short-wavelength synchrotron radiation to measure luminescence quantum yield and the luminescence excitation spectrum of polymers

We describe an optical diagnostics module and the instrumental and methodological features of ultrahigh vacuum experiments investigating the optical characteristics of condensed media in the short-wavelength (hv ~ 3.5–25 eV) range of the spectrum of probing synchrotron radiation. We give a brief presentation of the results of an experimental determination of the spectral dependence of the luminescence quantum yield and the luminescence excitation spectrum of ablatable polymer dielectrics on the Kurchatov synchrotron radiation source at values of the probing radiation power density (I ₀ ~ 10¹² photons/cm²∙sec) that are below threshold for extended surface vaporization and a surface temperature of the condensed targets equal to 77–300 K.     

Luminescence properties of calcium-iodide crystals

The effect of the conditions of preparation, temperature, and the action of x rays on the luminescence properties of calcium-iodide scintillation crystals is investigated. On the basis of the results of a study of the spectral characteristics of CaI₂ and CaI₂:H₂ crystals for optical and x-ray excitation in the temperature range 90–400 K, also taking into account the results of a study of the luminescence properties of CaI₂ crystals activated by Cl⁻, Br⁻, OH⁻, and Ca²⁺ impurities, it is suggested that the 236-nm band observed in the excitation spectra of crystals of calcium iodide may be caused by an uncontrollable hydrogen impurity. The luminescence of these crystals with maximum at 395 nm is ascribed to radiative recombination of excitons trapped at H⁻ ions. Zh. Tekh. Fiz. 69, 135–136 (January 1999)     

Luminescence properties of transparent ceramics Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Yb

We present the results of studying the luminescence properties of transparent ceramics Y₃Al₅O₁₂:Yb obtained by the vacuum sintering and nanocrystalline technology. In the course of research, we measured the luminescence and luminescence excitation spectra, as well as the temperature and kinetic behavior of luminescence. Our results are analyzed in comparison with the characteristics of corresponding single crystals. We revealed that processes of generation and relaxation of electronic excitations that occur in ceramics, in particular, in the charge transfer state, are similar to processes occurring in crystals. The behavior of two charge-transfer luminescence bands at 340 and 490 nm is studied. In the range 300–600 nm, we revealed a broad emission band of radiation of other type, which is also observed in spectra of undoped ceramics. This broad band is attributed to F⁺ centers. Emission and excitation spectra of charge transfer luminescence at a maximum of the temperature dependence of 100 K are measured for the first time. We found that, upon excitation in the charge transfer band, luminescence in ceramics is more intense than in single crystals with similar concentrations of Yb and has a higher quenching temperature.     

EPR and dielectric relaxation of Fe3+ in KTaO3

EPR and the method of dielectric losses have been used to investigate Fe³⁺ centers of axial and orthorhombic symmetry in KTaO₃ single crystals. The EPR spectrum of orthorhombic-symmetry Fe³⁺ obtained in the 8-mm wavelength range at T=77 K is described by the spin-Hamiltonian with parameters g _x=1.98, g _y=2.01, g _z=2.00, D=0.43 cm⁻¹, and E=5.87×10^t-2 cm⁻¹. From the dielectric measurement data we have obtained the following parameters of the relaxation of the orthorhombic Fe³⁺ centers in KTaO₃: characteristic relaxation frequency τ ₀ ⁻¹ =2.33×10¹² Hz and activation energy E _a=0.044 eV. A model of the orthorhombic Fe³⁺ center in KTaO₃ is discussed within the framework of the kinetic parameters obtained. Fiz. Tverd. Tela (St. Petersburg) 39, 861–864 (May 1997)     

Luminescence efficiency of aromatic carboxylates of europium and terbium when methylene bridges and nitro groups are present in the ligands

We discuss the possibility of optimizing the brightness of luminescence for phenylcarboxylates, naphthylcarboxylates, and indolylcarboxylates of europium and terbium and their adducts with 1,10-phenanthroline and 2,2′-bipyridine by modifying the ligands. We have studied the efficiency of luminescence and luminescence excitation. We consider the effect of blocking energy transfer from the ligands to the Eu³⁺ and Tb³⁺ ions by methylene (-CH₂-) bridges dividing the π-electron system of the ligands into two parts and by the electronacceptor nitro group (-NO₂). We have analyzed the pathways for transfer and degradation of the excitation energy at 77 K and 300 K. From the phosphorescence spectra of gadolinium salts, we have determined the energies of the lowest excited triplet states of the ligands. We consider the effect of the relative positions of the triplet levels of the ligands and the excited levels of the Eu³⁺ and Tb³⁺ ions on the luminescence efficiency. We found channels for dissipation of the excitation energy via the ππ* and nπ* states of the aromatic system of the carboxylate and the NO₂ group. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 48–54, January–February, 2007.     

Parametric excitation of temperature oscillations in a high-Q dielectric microwave resonator in liquid helium vapor

We study the threshold conditions of the parametric excitation of temperature oscillations using pulsed microwave pumping in three-mode regime for high-Q ferroelectric cryogenic resonators made of SrTiO₃ and KTaO₃. Comparative analysis is performed for the threshold power of the excitation of temperature oscillations and the threshold power of the ponderomotive parametric excitation of acoustic oscillations in the resonator. It is shown that in three-mode regime, temperature oscillations can develop under a rather moderate pump power of about 0.1–8 μW, depending on the combination of interacting temperature and electromagnetic modes. The calculated low threshold powers allow one to apply resonators in practice as high-sensitivity infrared sensors, resonant bolometers, and parametric amplifiers. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 2, pp. 172–180, February 2009.     

Ultrasonic investigation in KTaO3

The anomalous ultrasonic attenuationα _c of longitudinal waves propagating along (100) direction in KTaO₃ has been analyzed above the phase transition temperature in the frequency range 150–300 MHz in the paraelectric phase. The attenuation of longitudinal ultrasonic waves in KTaO₃ is primarily due to a strong interaction with thermally-excited phonons in the soft mode. Frequency and temperature variations of attenuation are discussed.     

Dielectric permittivity and phase transitions in the SrTiO3-KTaO3 system

The dielectric permittivity and losses of the (SrTiO₃)_0.85(KTaO₃)_0.15 solid solution have revealed an unusual behavior at temperatures of 5–300 K and frequencies ranging from 100 Hz to 1 MHz. The dielectric permittivity exhibits a broad maximum at ≈40 K, which obeys the Curie-Weiss law in the high-temperature wing, and the onset of low-temperature relaxation contributions. Besides, while for T>40 K it is a fully ergodic, uniformly ordering system, the uniform polar ordering is replaced with decreasing temperature by two low-temperature phase transitions to a glass-like state. The proposed mechanism for the dielectric relaxation and the observed phase transformations involves reorientation and ordering in the system of electron and hole polarons, which form in the course of charge compensation of the heterovalent ions Sr²⁺, K⁺ and Ti⁴⁺, Ta⁵⁺ distributed randomly in the sublattices. Fiz. Tverd. Tela (St. Petersburg) 39, 2040–2045 (November 1997)     

Luminescence detection of multiphoton ionization-fragmentation of the molecular CrO 4 2− anions adsorbed on the surface of dispersed SiO2

It is shown that luminescence detection of multiphoton ionization-fragmentation of the molecular CrO ₄ ²⁻ anions adsorbed on the surface of dispersed SiO₂ is possible under excitation with the fundamental frequency of a Nd:YAG pulsed laser (λ=1.064 μm). The structure and the process of formation of the adsorbed complexes under thermal activation of the surface and the nature of luminescence transitions in CrO ₄ ²⁻ anions are studied in detail. It is shown that luminescence is excited as a result of the recombination of photoelectrons and ionized chromate ions. Multiphoton ionization of the ions occurs under three-photon resonance conditions. The resonance level is an antibonding state of the adsorption complex formed with the participation of an oxygen vacancy on the SiO₂ surface. The dynamics of the multiphoton luminescence excitation process includes autoionization (stimulated by intercomplex electronic excitation) in superexcited states, fragmentation of chromate anions, and annealing of surface oxygen vacancies. The rate equations for three-photon-resonance multiphoton ionization are studied. The cross sections for two-and one-photon transitions on the nonresonance steps of multiphoton absorption are obtained. It is concluded that the nonlinear polarizability of the donor-acceptor adsorption bond in “chromate anion-oxygen vacancy” complexes is very important. Zh. éksp. Teor. Fiz. 111, 1748–1774 (May 1997)     

Self-trapping of the <Emphasis Type="Italic">d</Emphasis>-<Emphasis Type="Italic">d</Emphasis> charge transfer exciton in bulk NiO evidenced by X-ray excited luminescence

Soft X-ray (XUV) excitation did make it possible to avoid the predominant role of the surface effects in luminescence of NiO and revealed a bulk luminescence with a puzzling well isolated doublet of very narrow lines with close energies near 3.3 eV which is assigned to recombination transitions in self-trapped d-d charge transfer (CT) excitons formed by coupled Jahn-Teller Ni⁺ and Ni³⁺ centers. The conclusion is supported both by a comparative analysis of the CT luminescence spectra for NiO and solid solutions Ni _x Zn_{1 − x} O, and by a comprehensive cluster model assignment of different p-d and d-d CT transitions, their relaxation channels. To the best of our knowledge, it is the first observation of the luminescence due to self-trapped d-d CT excitons.     

Polar state in a SrTiO3-KTaO3 solid solution

Dielectric properties of ceramic samples of a 0.85SrTiO₃-0.15KTaO₃ solid solution have been studied. The temperature dependence of the dielectric permittivity exhibits maxima with a strong frequency dispersion, which is described by the Vogel-Fulcher law with a characteristic temperature T _g=26 K. These features are apparently connected with transition to a polar glasslike state. Fiz. Tverd. Tela (St. Petersburg) 39, 1838–1840 (October 1997)     

Polarization dependence of luminescence induced by two-photon excitation in LiF crystals with F 3 + laser color centers and the symmetry of the excited state

The energy level structure of F ₃ ⁺ laser color centers in crystals of LiF is discussed. A high-power laser (λ _ex=920 nm) is used to excite luminescence from LiF crystals with F ₃ ⁺ centers via two-photon absorption, and the dependence of the polarization and intensity of this luminescence on the polarization of the laser light is measured and calculated. It is shown that the two-photon transition involves the excitation of a previously unknown state of the F ₃ ⁺ center—a spin singlet whose wave function has ¹ A ₁ symmetry. Fiz. Tverd. Tela (St. Petersburg) 39, 1373–1379 (August 1996)     

Evidence for exciton binding at Ni impurity sites in ZnSe

A broad charge transfer band is observed in the photoluminescence excitation (PLE) spectrum of the 2.5 μ Ni²⁺ luminescence in ZnSe : Ni. This band lies above the highest energy d-d excitation bands and exhibits a ZPL at 1.8163 eV and LO(#38;0lambda;) phonon replicas at higher energy. In contrast, PLE spectra of Co²⁺ luminescence in ZnSe:Co contain only d-d excitation bands. The charge transfer band in ZnSe:Ni is interpreted as evidence for bound exciton formation at the Ni site. The recombination energy of this exciton is transferred efficiently to the excited d-band states of the Ni ion, leading to characteristic Ni²⁺d-d luminescence.     

Analysis of the latent structure of luminescence and absorption spectra of thallium complexes

Comprehensive investigations of luminescence, excitation, and absorption spectra as well as of the luminescence kinetics of a frozen LiCl-Tl⁺ solution are carried out. It is established that the luminescence spectrum consists of four components. One component is caused by luminescence of the matrix and the remainder by luminescence of one luminescence center, namely, by the saturated complex of thallium TlCl₂(H₂O)Cl₄. The absorption spectrum consists of three components. Their parameters have been evaluated. Each component of the luminescence spectrum is excited in several components of the absorption spectrum. It is found that the luminescence spectrum components and their intrinsic absorption bands are located differently on the frequency axis. These data are similar to those obtained for other activated solutions of electrolytes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 75–78, January–February, 2000.     

Recombination kinetics in nonlinear defective LiB3O5 crystals

A study of recombination kinetics in LiB₃O₅ (LBO) crystals by time-resolved luminescence and absorption spectroscopy is reported. An investigation of the kinetics of transient optical absorption (TOA) and luminescence under ns-scale electron-beam excitation performed within a broad temperature range of 77–500 K and a 1.2–5-eV spectral interval has established that the specific features in the recombination kinetics observed in LBO involve electronic, B²⁺, and hole, O⁻, trapping centers. The TOA and luminescence kinetics, as well as their temperature dependence, are interpreted by a model of competing hole centers. Relations connecting the kinetics parameters and the temperature dependence to the parameters of the main LBO point defects are presented. Fiz. Tverd. Tela (St. Petersburg) 40, 2008–2014 (November 1998)